1. Field of the Invention
The present invention relates to a sheet aligning device, a sheet processing device, and an image forming apparatus.
2. Description of the Related Art
For center stapling, sheet finishers align sheets in a stapling unit and position them at the same place to staple the sheets, and convey the center-stapled sheets to a folding unit downstream. Although the maximum stapling capacity of approximately 50 sheets has been sufficient, there has been a recent demand for a stapling capacity of 100 sheets. When the stapling capacity is increased to meet the demand, staplers are also increased in size, which makes a layout of a center stapler and a center-folding mechanism difficult.
More specifically, in a conventional sheet finisher with a stapling capacity of 50 sheets, as described above, the center stapler is positioned in the stapling unit, and stapling can be performed on sheets by aligning the sheets with a jogger fence, which is commonly used for both edge stapling and center stapling. The shared use of the jogger fence is allowed thanks to a conveyance capacity of 50 sheets, corresponding the maximum stapling capacity, through between a clincher and a driver (distance set for the clearance between the clincher and the driver is 15 millimeters) of the center stapler.
Such a sheet finisher is described in, for example, Japanese Patent Application Laid-open Nos. H10-181987, 2000-118850, and 2003-073022.
When the center stapler is positioned in a stapling unit having a stapling capacity of 100 sheets as in the case of a stapling unit having a stapling capacity of 50 sheets, it is physically impossible to convey 100 sheets, corresponding to the maximum stapling capacity, through clearance space between the clincher and the driver of the center stapler. Thus, the sheets cause jam by blocking the clearance space. Meanwhile, when a stack of sheets is aligned in the stapling unit as performed in the conventional device, because the width of a jogger fence of the conventional stapling unit is set for the maximum stapling capacity, i.e., 50 sheets, a large space allowance is produced. The large space allowance sometimes causes the sheets to flutter, and stapling positions to vary. In other words, due to the large space allowance, control against curling or bending of the sheets sometimes fails, which also causes stapling at an intended position to fail.